JPS62146500A - Read-only memory - Google Patents

Abstract

PURPOSE:To check a syndrome output by extracting the syndrome directly from an output terminal. CONSTITUTION:In accordance with a switching signal obtained from a mode switching terminal 9, a mode switching circuit 8 switches a normal mode for selecting data read out from a data ROM 3' through an error correcting circuit 6' and corrected at its error through a testing ROM 4', a syndrome forming circuit 5', etc., to a mode for selecting a syndrome output from the circuit 5'. In the mode, the syndrome output can be directly extracted from the output terminal 7' to check the syndrome output and whether error correction is executed or not and the error data in the ROMs 3', 4' at the execution of the error correction can be detected, so that search of the cause of a defect or a counterplan for the defect can be properly executed.

Description

[Detailed Description of the Invention] [Technical Field] The present invention relates to a read-only memory, and in particular, to a read-only memory, in particular, when a part of stored data is used as redundancy and an error occurs in a part of the stored data. The present invention relates to a read-only memory with a built-in error correction circuit that corrects errors.

[Prior art]

Read-only memory (hereinafter referred to as ROM) is widely used for storing computer programs and data. In recent years, the degree of integration of ROM has improved, and the amount of data that can be stored per chip has increased.In order to prevent the chip from becoming defective due to a slight error, some of the stored data is Even if an error occurs in a part of the output data, an error correction circuit is built in to correct the error and improve yield.

FIG. 1 is a block diagram showing the main parts of an example of a conventional ROM. In Figure 1, 1 is an address input terminal, 2 is an address decoder, 3 is a data ROM, and 4 is a test RO.
M15 is a syndrome generation circuit, 6 is an error correction circuit, 7
is the output terminal.

The address input from the address input terminal 1 is divided into data bits and test bits by the address decoder 2, which are respectively stored in the data ROM 3 and the test ROM 4.
to go into. Enter data ROM3 and test ROM4. Data output from data ROM3 and inspection ROM4
The data outputted from the is input to the syndrome generation circuit 5, a syndrome is generated, and the error correction circuit 6 generates a syndrome.
The output data is corrected and the data is output from the output terminal 7.

However, although error correction is possible with this method, it is difficult to determine whether the output data is error-corrected data or not, and if the data is error-corrected, which bits are incorrect? The drawback was that it was difficult to determine whether the

[Purpose of the invention]

SUMMARY OF THE INVENTION In view of the above drawbacks, an object of the present invention is to provide a read-only memory that allows a syndrome generated by a syndrome generation circuit to be output directly from an output terminal.

[Structure of the invention]

The read-only memory of the present invention includes a selection means capable of appropriately switching between a normal mode in which error-corrected ROM data is output and a syndrome output mode in which syndrome contents are directly output. be done.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 2 is a block diagram showing one embodiment of the present invention.

In FIG. 2, 1' to 7' correspond to 1 to 7 shown in FIG. 8 is a mode switching circuit, and 9 is a mode selection signal input terminal.

The mode switching circuit 8 is controlled by the input of the mode selection signal input terminal 9, and the error-corrected RO is set to the normal mode.
It is possible to select a mode of outputting M data or outputting a syndrome as a syndrome output mode. This allows you to check for syndromes,
Whether or not error correction has been performed on the output data, and if error correction has been performed, on which information data, and even if the information data has no errors and error correction has not been performed, It is possible to know whether or not there is an error in the data, and if so, which test data it is.

〔Effect of the invention〕

As explained above in detail, the read-only memory of the present invention, with the above configuration, can check the output of the syndrome, so even if the chip is considered to be a good product, it can be checked whether error correction has been performed or not. If this is done, it will be possible to know which data is incorrect in the information data memory and the inspection data memory, so it will be possible to take measures to find the cause of the defect, and as a result, the yield of the product can be improved. can get.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the main parts of an example of a conventional read-only memory, and FIG. 2 is a block diagram showing the main parts of an embodiment of the present invention. 1.1'...address input terminal, 2.2'...
... Address decoder, 3, 3'... Data ROM, 4, 4'... Test ROM, 5,
5'...Syndrome generation circuit, 6,6'...
...Error correction circuit, 7, 7'...Output terminal, 8...Mode switching circuit, 9...Mode selection signal input terminal.

Claims (1)

[Claims] At least an information data memory, a test memory, a syndrome generation circuit, and an error correction circuit are mounted on one chip, and even if an error occurs in a part of the stored information data memory or test memory, the information data memory and test By generating a syndrome in the syndrome generation circuit from the contents of the storage memory and inputting the syndrome and information data to the error correction circuit, it is possible to correct even if an error occurs in a part of the stored data. A read-only memory characterized by having means for directly outputting a syndrome from an output terminal.